Temperable three layer antirefrlective coating, coated article including temperable three layer antirefrlective coating, and/or method of making the same

ABSTRACT

A coated article includes a temperable antireflection (AR) coating that utilizes medium and low index (index of refraction “n”) layers having compressive residual stress in the AR coating. In certain example embodiments, the coating may include the following layers from the glass substrate outwardly: silicon oxynitride (SiO x N y ) medium index layer/high index layer/low index layer. In certain example embodiments, depending on the chemical and optical properties of the high index layer and the substrate, the medium and low index layers of the AR coating are selected to cause a net compressive residual stress and thus optimize the overall performance of the antireflection coating when the coated article is tempered and/or heat-treated.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) of U.S. applicationSer. No. 12/923,146, the entire contents of which are herebyincorporated herein by reference.

FIELD OF THE INVENTION

Certain example embodiments of this invention relate to a coated articleincluding a temperable antireflective coating, and/or a method of makingthe same. In certain example embodiments, a temperable antireflective(AR) coating utilizes SiO_(x)N_(y) as the medium index layer of thecoating. In certain example embodiments, the coating may include thefollowing layers from the glass substrate outwardly: silicon oxynitride(e.g., SiO_(x)N_(y)) as the medium index layer/titanium oxide (e.g.,TiOx) as the high index layer/silicon oxide (e.g., SiOx) as the lowindex layer. In certain example embodiments, the thicknesses and/ortypes of stress in each layer may be optimized in order to produce atemperable, three layer antireflective coating.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Antireflective (AR) coatings are known in the art. For example, ARcoatings in the visible range are widely used on glass in electronics,lighting, appliances, architectural, and display applications. There arevarious techniques for reducing the reflection of visible light movingfrom air onto and through a glass surface. One technique is to apply athin layer of material onto the surface of a glass substrate,interposing the thin layer between the glass substrate and the air.Optimally, the index of refraction of the thin layer is equal to thesquare root of the product of the index of refraction of visible lightthrough air and the index of refraction of visible light through theglass substrate. Achieving this optimal index of refraction is difficulthowever.

Further, in many of these applications, tempered or heat-strengthenedglass may be required. Tempering or heat strengthening of the glass issometimes done prior to the deposition of the AR coating to avoidunwanted changes in the optical, mechanical, or aesthetic quality of thecoating as a consequence of exposing the coating to the hightemperatures required for tempering and other forms of heat treatment.However, this “temper then coat” method may be undesirable in certaincircumstances.

Further, a coat then temper technique may create additional problems.When glass is coated and then tempered, the result of the temperingprocess may produce undesirable optical flaws in the overall glassproduct. For example, the color shift, or ΔE, in the tempered, coatedglass product may render the glass unusable. Further, techniques thatmaintain the optical characteristics of a substrate with an AR betweenpre and post tempering are desirable (e.g., one AR coating may beapplied in more than one situation).

Thus, it will be appreciated that there exists a need in the art forimproved antireflective (AR) coatings (e.g., temperable AR coatings) forcoated articles such as windows and the like.

In certain example embodiments, there is provided a coated articlecomprising an antireflective coating supported by a major surface of asubstrate, the substrate being heat treated together with theantireflective coating, wherein the antireflective coating comprises, inorder moving away from the substrate: a medium index layer comprisingsilicon oxynitride and having a index of refraction of from about 1.65to 2.0 at 380 nm, 550 nm, and 780 nm wavelengths, a high index layerhaving an index of refraction of at least about 2.0 at 380 nm, 550 nm,and 780 nm wavelengths, and a low index layer having an index ofrefraction of from about 1.4 to 1.6 at 380 nm, 550 nm, and 780 nmwavelengths, wherein the medium index layer has compressive residualstress after heat treatment.

In certain example embodiments, there is provided a heat treatablecoated article, the coated article comprising: an antireflective coatingsupported by a major surface of a substrate, wherein the antireflectivecoating comprises, in order moving away from the substrate: a mediumindex layer comprising silicon oxynitride and having a index ofrefraction of from about 1.65 to 2.0 at 380 nm, 550 nm, and 780 nmwavelengths, a high index layer having an index of refraction higherthan that of the medium index layer at 380 nm, 550 nm, and 780 nmwavelengths, and a low index layer having an index of refraction lowerthan that of the medium index layer at 380 nm, 550 nm, and 780 nmwavelengths, wherein the medium index layer and the low index layer havecompressive residual stress after any heat treatment, the high indexlayer has tensile residual stress after any heat treatment, and theantireflective coating has a net compressive residual stress.

In certain example embodiments, there is provided a heat treatablecoated article, the coated article comprising an antireflective coatingsupported by a major surface of a substrate, wherein the antireflectivecoating comprises, in order moving away from the substrate: a mediumindex silicon-inclusive layer having a index of refraction of 1.8 orless 550 nm and 780 nm wavelengths and 2.0 or less at 380 nm, a highindex layer having an index of refraction higher than that of the mediumindex layer at 380 nm, 550 nm, and 780 nm wavelengths, wherein the highindex layer has a thickness no greater than about 20 nm, and a low indexlayer having an index of refraction lower than that of the medium indexlayer at 380 nm, 550 nm, and 780 nm wavelengths, wherein the mediumindex layer and the low index layer have compressive residual stress,the high index layer has tensile residual stress, and the antireflectivecoating has a net compressive residual stress.

In certain example embodiments, there is provided a method of making acoated article with a three-layered antireflection coating, the methodcomprising: disposing a medium index layer, directly or indirectly, on aglass substrate; disposing a high index layer over and contacting themedium index layer; disposing a low index layer over and contacting thehigh index layer; and heat-treating the glass substrate with theantireflective coating thereon, and wherein the coated article has a netcompressive residual stress.

In certain example embodiments, a method of making a coated article isprovided. A glass substrate is provided. A silicon-inclusive mediumindex layer is disposed, directly or indirectly, on a first majorsurface of the substrate. A high index layer is disposed over andcontacting the medium index layer, the high index layer having athickness of at least 85 nm. A low index layer is disposed over andcontacting the high index layer. The substrate is heat treated with themedium, high, and low index layers disposed thereon. The coated articlehas a ΔE* value of less than 3 between as deposited and heat treatedstates.

In certain example embodiments, a method of making a coated article isprovided. A glass substrate is provided. A silicon-inclusive mediumindex layer is disposed, directly or indirectly, on a first majorsurface of the substrate. A high index layer is disposed over andcontacting the medium index layer, the high index layer having athickness of at least 85 nm. A low index layer is disposed over andcontacting the high index layer. The coated article is heat treatable soas to have a ΔE* value of less than 3.

In certain example embodiments, a coated article comprising anantireflective coating supported by a first major surface of a substrateis provided. The antireflective coating comprises, in order moving awayfrom the substrate: a silicon-inclusive medium index layer disposed,directly or indirectly, on the first major surface of the substrate; ahigh index layer disposed over and contacting the medium index layer,the high index layer having a thickness of at least 85 nm; and a lowindex layer disposed over and contacting the high index layer. Thecoated article is heat treatable so as to have a ΔE* value of less than3.

According to certain example embodiments, A second major surface of thesubstrate may support a second antireflective coating that comprises, inorder moving away from the substrate: a second silicon-inclusive mediumindex layer, directly or indirectly, on the second major surface of thesubstrate; a second high index layer over and contacting the secondmedium index layer, the high index layer having a thickness of at least85 nm; and a second low index layer over and contacting the second highindex layer. All said layers may be disposed on the substrate prior toany heat treating. In such example embodiments, the ΔE* value may beless than 2 and sometimes less than or equal to about 1.5.

The features, aspects, advantages, and example embodiments describedherein may be combined to realize yet further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is an example of a three-layered temperable AR coating generallyaccording to certain example embodiments of this invention;

FIG. 2 is an example of an optimal three-layered temperable AR coatingmade according to certain example embodiments of this invention;

FIG. 3 is an example of a two-sided temperable AR coating made accordingto certain example embodiments of this invention;

FIG. 4 is a graph of the first surface reflectivity comparison of an ARcoating before and after exposure to a tempering environment;

FIG. 5 is a graph showing changes in the reflectivity between theas-deposited and tempered states compared to the tristimulus values usedin the color calculations;

FIG. 6 is a table showing the as-coated visible transmission and colorcharacteristics of an AR coating made according to certain exampleembodiments of this invention;

FIG. 7 is a table showing the resulting optical qualities of an ARcoating made according to certain example embodiments of this inventionafter exposure to 650 degrees C. for 10 minutes;

FIG. 8 is a table showing examples of the compressive and tensilestresses than can arise in different layers, both as-deposited and afterheat-treatment and/or tempering;

FIG. 9 is a graph showing the residual stress for coatings with varioustitanium oxide thicknesses;

FIG. 10 is a graph comparing the light transmission of a coated articlemade according to examples described herein, before and after exposureto a tempering environment;

FIG. 11 is a table showing example optimal thicknesses and refractiveindices for AR coatings made according to certain example embodiments ofthis invention;

FIG. 12 is an example of a three-layered temperable AR coating madeaccording to certain example embodiments;

FIG. 13 is an example of a two-sided temperable AR coating madeaccording to certain example embodiments;

FIG. 14 is a graph showing the surface reflectivity comparison of athree-layer AR coating before and after exposure to a temperingenvironment according to certain example embodiments;

FIG. 15 is a graph showing the color shift before and after temperingusing SiOxNy as the middle index layer adjacent to the glass substrateaccording to certain example embodiments; and

FIG. 16 is a graph showing the surface reflectivity comparison of athree-layer AR coating applied to both surfaces of a glass substratebefore and after exposure to a tempering environment according tocertain example embodiments.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Referring now more particularly to the accompanying drawings in whichlike reference numerals indicate like parts throughout the severalviews.

Certain example embodiments of this invention relate to a coated articleincluding an antireflective coating, and/or a method of making the same.In certain example embodiments, a temperable antireflective (AR) coatingis provided.

As indicated above, AR coatings in the visible range are widely used onglass in electronics, lighting, appliances, architectural, and displayapplications. Although tempering or heat strengthening of the glass issometimes done prior to the deposition of the AR coating to avoidunwanted changes in the optical, mechanical, or aesthetic quality of thecoating as a consequence of exposing the coating to the hightemperatures required for tempering and other forms of heat treatment,there are drawbacks associated with the “temper then coat” method undercertain example circumstances. For example, tempering prior to coatingmay be undesirable for large area coaters. The final size of thetempered/heat treated substrate to be coated may be of a dimension thatdoes not efficiently employ the large area coating capability, which isuseful when attempting to increase achieve the high efficienciespossible by virtue of high volume glass coating manufacturingtechniques.

When the AR coating is applied prior to tempering other problems in themanufacturing process may develop. For example, for a three layervisible anti-reflective coating, it sometimes is desirable to have arefractive index on the layer immediately adjacent to the glasssubstrate of between about 1.65 and 2.0. However, while there arecertain materials that do possess such properties, using these materialsin a three-layer coating may or may not result in undesirable colorshifts and degradation in the spectral response of the coating afterexposure to typical tempering environments. Thus, certain materialsutilized in AR coatings may show a change in spectral response aftertempering and thus may cause an undesired color shift relative to the“as deposited” form of the coating.

Therefore, it will be appreciated that a three-layered antireflectivecoating that can be tempered and/or heat treated while preserving itsaesthetic quality and high chemical and mechanical durability afterexposure to temperatures typically encountered in tempering and/or heattreating environments would be advantageous.

Existing three layer AR coatings may not be sufficiently temperable incertain example embodiments, e.g., in the sense that such coatings maynot survive the tempering process in a usable or desirable form. As oneexample, it is noted that some materials utilized in AR coatings mayhave high tensile residual stress after exposure to temperatures greaterthan, for example, 300 degrees C. When the tensile residual stress ofone layer is so high such that it results in a net tensile stress in themultilayer stack, this stress may be sufficient to cause an aestheticdegradation of the coating. This and/or similar problems may, forexample, result in the cracking of the coating. Therefore, it may beadvantageous to reduce the tensile residual stress in a layer in an ARcoating, offset the tensile residual stress by reducing the thickness ofthat layer, balance the tensile residual stress in one layer withcompressive residual stress in the other layer(s), etc.

Compressive stress, when applied, acts toward the center of a material.Thus, when a material is subjected to compressive stress, the materialis under compression. When a material is subjected to tensile stress, onthe other hand, the material may suffer stretching or elongation.Accordingly, if too much tensile residual stress is present in a layerin a coating, the layer and/or coating may suffer deformation orcracking in certain instances. Therefore, in certain exampleembodiments, it may be more desirable for a coating to have a netcompressive residual stress rather than a net tensile residual stress.

FIG. 1 is a cross sectional view of an example coated article accordingto an example embodiment of this invention. The coated article of theFIG. 1 embodiment includes substrate 1 that supports temperableantireflective (AR) coating 3. Substrate 1 is typically a glasssubstrate (e.g., clear, green, bronze, or blue-green glass substratefrom about 1.0 to 10.0 mm thick), but may be other materials in certainexample instances such as polycarbonate or acrylic. The AR coating 3includes medium index layer 5, high index layer 7, and low index layer9. The medium, high, and low index layers 5, 7, and 9 may be provided inthis order moving away from the substrate 1 in certain exampleembodiments of this invention. Furthermore, in certain exampleembodiments, the layers may directly contact one another. In thisexample embodiment, the low index layer 9 is the outermost layer of thecoating 3, whereas the medium index layer 5 is the bottom-most layer ofthe AR coating 3. The AR coating 3 is a dielectric type coating in thateach of layers 5, 7 and 9 is a dielectric layer (i.e., not electricallyconductive). Thus, the AR coating 3 of the FIG. 1 example embodiment hasno IR reflecting layer (i.e., no metallic layer of Ag, Au, or the like),and no transparent conductive oxide (TCO) layer such as a pyrolyticallydeposited metal oxide/nitride. Of course, it will be appreciated thatlow-E coatings may be used in connection with different embodiments ofthis invention, e.g., in combination with the AR coating 3 on the sameor opposite side of the substrate 1.

In certain example embodiments of this invention, a temperable ARcoating includes at least three dielectric layers, namely a high indexlayer, a medium index layer and a low index layer. The meanings of“high”, “medium” and “low” are simply that the medium index layer has anindex of refraction (n) less than that of the high index layer andgreater than that of the low index layer (e.g., no specific values arerequired merely by the use of “high”, “medium” and “low”). The high,medium, and low index layers are typically dielectric layers in certainexample embodiments of this invention, in that they are not electricallyconductive.

The refractive index (n) of medium index layer 5 is less than therefractive index of the high index layer 7 and greater than therefractive index of the low index layer 9. In certain exampleembodiments, the low index layer 9 may be of or include silicon or anoxide thereof (e.g., SiO₂ or other suitable stoichiometry), MgF, ortheir alloyed oxide and fluoride. In certain example embodiments, thehigh index layer 7 may be of or include a metal oxide, metal nitrideand/or metal oxynitride such as titanium oxide (e.g., TiO₂ or othersuitable stoichiometry), zinc oxide, silicon or a nitride thereof, orthe like.

The AR coating of FIG. 2 is the same as the AR coating of FIG. 1, butinstead shows example materials used for each of the medium, high, andlow index layers.

In certain example embodiments of this invention, the medium index layer5 is a bottom layer of the AR coating and has an index of refraction (n)of from about 1.60 to 2.0, more preferably from about 1.65 to 1.9, evenmore preferably from about 1.7 to 1.8, and most preferably from about1.7 to 1.79 (at 550 nm). At 380 nm, in certain example embodiments, anideal refractive index of medium index layer 5 is from about 1.8 to 2.0.In further example embodiments, the index of refraction of medium indexlayer 5 is from about 1.65-1.8 at 780 nm.

In certain instances, it is advantageous that the material(s) comprisingmedium index layer 5 have desired optical and mechanical properties inthe as-deposited state as well as after exposure to temperatures typicalin tempering and/or heat treating environments. It will be appreciatedthat materials such as aluminum oxynitride, though having desiredproperties in the as-deposited state, may degrade in optical and/ormechanical properties after exposure to temperatures typical intempering and/or heat treating environments. Aluminum oxynitride may,however, be used in different embodiments of this invention if it can bemade to be sufficiently survivable.

Furthermore, it is advantageous if the medium index layer 5 has acompressive residual stress in both the as-coated and heat-treatedstates. In certain example embodiments, this compressive residual stressmay help to offset the tensile residual stress in the other layer(s) inthe stack. In certain instances, this may promote a net compressivestress in the three layer AR stack, which discourages cracking of thecoating during the tempering and/or heat treating processes.

Medium index layer 5 preferably has a thickness of from about 75 to 135nm, more preferably from about 80 to 130 nm, even more preferably fromabout 89 to 120 nm, and most preferably from about 94 to 115 nm.

It has surprisingly been found that silicon oxynitride (e.g., SiOxNy)can be deposited to have an index of refraction of from about 1.60 to2.0, more preferably from about 1.65 to 1.9, even more preferably fromabout 1.7 to 1.85 or 1.7 to 1.8, and most preferably from about 1.7 to1.79 (at 550 nm), and will not significantly degrade in its mechanicalor optical properties upon tempering and/or heat treatment. Moreover, incertain example embodiments, a layer of or comprising silicon oxynitride(e.g., SiOxNy) advantageously has a compressive residual stress in boththe as-coated and heat-treated states. Therefore, it has advantageouslybeen found that a layer of or including silicon oxynitride (e.g.,SiOxNy) is suitable for use as a medium index layer 5 in a temperablethree layer AR coating.

In certain example embodiments of this invention, the high index layer 7is provided over the medium index layer 5 of the AR coating 3. Layer 7has an index of refraction of at least about 2.0, preferably from about2.1 to 2.7, more preferably from about 2.25 to 2.55, and most preferablyfrom about 2.3 to 2.5 (at 550 nm) in certain example embodiments. Incertain example embodiments, an ideal index of refraction of high indexlayer 7 at 380 nm may be from about 2.7 to 2.9 (and all subrangestherebetween). In further example embodiments, an ideal index ofrefraction of high index layer 7 at 780 nm may be from about 2.2 to 2.4(and all subranges therebetween).

High index layer 7 preferably has a thickness of from about 5 to 50 nm,more preferably from about 10 to 35 nm, even more preferably from about12 to 22 nm, and most preferably from about 15 to 22 nm. In certainexemplary embodiments, the high index layer 7 has a thickness of lessthan about 25 nm.

In certain instances, it is advantageous that the material(s) comprisinghigh index layer 7 have a high index of refraction. An example materialfor use as a high index layer is titanium oxide (e.g., TiOx). However,in certain example embodiments, titanium oxide has a high tensileresidual stress after exposure to temperatures above 300 degrees C. Thehigh tensile stress in this layer is associated with a phase change fromamorphous to crystalline, observed between the as-coated and as-heattreated states. This phase change, in certain instances, occurs at atemperature below the maximum temperature of exposure of the coatingduring a typical tempering and/or heat treating process. The greater thethickness of the titanium oxide-based layer, the greater the tensileresidual stress. Depending on the thickness of the titanium oxide-basedlayer (e.g., TiOx), the high tensile residual stress in the titaniumoxide-based layer can case an overall large net tensile stress in thethree layer stack.

Therefore, it will be advantageous in certain instances if a temperableAR coating including a high index layer of or including titanium oxide(e.g., TiOx) comprises other layers (e.g., medium index layer and/or lowindex layer) having and/or promoting net compressive residual stressafter tempering and/or heat treating, in order to offset the hightensile stress of titanium oxide based layer after exposure to hightemperatures. In other instances, it is further advantageous if thephysical thickness of the high index titanium oxide-based layer 7 (e.g.,TiOx) can be reduced, while still maintaining the appropriate range ofoptical thicknesses to achieved desired optical properties of thetemperable AR coating. In certain example embodiments, this willadvantageously reduce the net tensile stress of the layer, and maypromote a net compressive residual stress for the overall coating. Inother words, in certain example embodiments, when the physical thicknessof the titanium oxide-based layer is limited, and the other layers areof materials having compressive residual stresses after tempering and/orheat treatment, it has surprisingly been found that a chemically andmechanically durable tempered coated article with good antireflectiveproperties can be achieved.

In certain example embodiments of this invention, the low index layer 9is provided over the high index layer 7 of the AR coating 3. Layer 9 hasan index of refraction of from about 1.4 to 1.6, more preferably fromabout 1.45 to 1.55, and most preferably from about 1.48 to 1.52 (at 550nm) in certain example embodiments. In certain example embodiments, anideal index of refraction of low index layer 9 at 380 nm may be fromabout 1.48 to 1.52 (and all subranges therebetween). In further exampleembodiments, an ideal index of refraction of low index layer 9 at 780 nmmay be from about 1.46 to 1.5 (and all subranges therebetween).

In certain example embodiments, low index layer 9 has a thickness offrom about 70 to 130 nm, more preferably from about 80 to 120 nm, evenmore preferably from about 89 to 109 nm, and most preferably from about100 to 110 nm.

In certain instances, it is advantageous that the material(s) comprisinglow index layer 9 have an index of refraction lower than both the mediumand high index layers, and in certain example embodiments, therefractive index of low index layer 9 may be less than that of the glasssubstrate upon which the coating is provided. An example material foruse as a low index layer is silicon oxide (e.g., SiOx).

The use of silicon oxide (e.g., SiOx) as the low index layer in atemperable three layer AR coating in certain example embodiments isadvantageous because silicon oxide has a low refractive index, and highchemical and mechanical durability. Additionally, in certain exampleembodiments, a low index layer based on silicon oxide advantageously hasa compressive residual stress in both the as-coated andheat-treated/tempered states. In certain example embodiments, thecompressive residual stress in a low index layer based on silicon oxidemay help to offset the tensile residual stress in the titaniumoxide-based layer. Utilizing a low index layer with compressive residualstress in conjunction with a high index layer with high tensile residualstress helps to promote a net compressive stress in a temperable threelayer AR stack in certain example embodiments. This is advantageous inthat it may help discourage cracking of the AR coating 3 duringtempering and/or heat treating the coated article in certain exampleembodiments.

The AR coating 3 of FIGS. 1 and 2 may be provided on only one majorsurface of glass substrate 1 as shown in FIGS. 1 and 2. However, FIG. 3illustrates an example embodiment of this invention where the coating 3is provided on both the major surfaces of the glass substrate 1. Inother words, a first AR coating 3 is provided on a first major surfaceof the substrate 1 and a second AR coating 3 is provided on a secondmajor surface of the substrate 1.

In certain example embodiments, the temperable AR coating may bedesigned to reduce undesired reflection. In most cases, reducedreflection comes with increased transmission such as AR on picture frameglass that a higher than 98% transmission is desired. However, theincreased transmission may not always be desired. For example, the ARcoating in the area overlapped with black matrix in a display wouldbenefit from a reflectivity that is as low as possible, but transmission(T) is relatively unimportant. In other words, as will be appreciated bythose skilled in the art, the transmission depends at least in part onthe substrates and/or applications.

Coated articles with antireflection coatings 3 are useful in certainwindow applications as mentioned herein. In this respect, coatedarticles according to certain example embodiments of this invention mayhave a visible transmission of at least about 50%, more preferably of atleast about 60%, and most preferably of at least about 70%. Such windowsmay be monolithic window glazings, insulating glass (IG) units, vacuuminsulating glass (VIG) units, and/or the like. In IG and/or VIG exampleapplications, the one or more substrates may support the antireflectivecoating 3 as shown and described herein.

EXAMPLES Example 1

An Example AR coating 3 was made as follows: SiO_(x)N_(y) layer 5(medium index layer) about 95 nm thick, TiO₂ layer 7 (example high indexlayer) about 21 nm thick, and SiO₂ layer 9 (example low index layer)about 105 nm thick. The clear glass substrate was about 5 mm thick, andwas soda lime silica type glass. Each of layers 5, 7, and 9 wasdeposited on the glass substrate 1 by sputtering a target(s). Thecoating 3 was provided on only one major surface of the glass substratein certain instances as shown in FIG. 1, but may be provided on bothmajor surfaces of the glass substrate in other instances as shown inFIG. 3. The coating was tempered at 650 degrees C. for 10 minutes.

FIG. 4 is a graph showing a comparison of the first surface reflectivityof an as-coated and a tempered/heat-treated three layer visible ARcoating at an 8 degree incident angle using White Light. FIG. 4illustrates the reflection spectra of an example having SiOxNy adjustedto achieve a refractive index for the medium index layer 5 of from about1.7-1.8 (at 550 nm), on one major surface of the glass substrate. It canbe seen that excellent AR characteristics (e.g., low R %) are achievedin a wavelength range of from about 450 to 650 nm, and even more so fromabout 500 to 600 nm. The design minimizes or reduces photopic reflection(CIE-C, 2°), and the measured value was less than 0.4%. In certainexample embodiments of this invention, the coated article has a photopicreflection of less than about 3.0%, more preferably less than about1.0%, more preferably less than about 0.5%, and most preferably lessthan about 0.25%.

FIG. 5 is a graph showing the change in the reflected spectral response(AR=R tempered−R as-coated) between the as-deposited andtempered/heat-treated coating in comparison to the tristimulus valuesused in the color calculations. The largest changes in the reflectivityoccur in regions where the tristimulus values are close to zero. Thisresults in a reduced amount of change in the reflected color between theas-coated and tempered/heat-treated states. This consideration isindependent of the source illuminant.

FIG. 6 is a table showing the as-coated visible reflection, visibletransmission, and color values at normal incidence (Ill. 2° C.) (withbackside reflection).

FIG. 7 is a table showing the resulting optical quantities of thesamples in FIG. 6 after exposure to 650 degrees C. for 10 minutes.

FIGS. 6 and 7 can be used to compare the change in the opticalquantities indicated between the as-coated and heat-treated/temperedstates. The optical quantities shown are for three substantially equallyspaced cross-coater positions (P,C,V) across a total width of 96 inches.Of course, the number of coater positions, their locations, and/or thetotal width may vary in different embodiments of this invention. Upontempering, there was an increase in the visible transmission, reductionof visible reflection, and a very small (ΔE*<2) reflected color shift.The color is considered within the industry standard after exposure to atempering environment.

FIG. 8 is a table showing additional data regarding the stress incertain example embodiments of a three-layer temperable AR coating. FIG.8 contains information about a coating made in a similar manner toExample 1, as well as comparative examples, but does not necessarilyreflect information from Example 1 itself. The first coating (a) in FIG.8 is a three-layer AR coating made according to certain exampleembodiments of this invention, and gives the values and types of the netresidual stress in the coating as-deposited, and after heat-treatingand/or tempering at 650 degrees C. for 10 minutes. The negative valuesfor σ_(x) and σ_(y) are indicative of the stress being compressive.Positive values, on the other hand, indicate tensile stress. In coatings(a), (b), and (c), it can be seen that the as-deposited net residualstress values are all negative. Therefore, as-deposited, each of thesecoatings has a net compressive residual stress. However, uponheat-treating and/or tempering, the stress in these coatings moves moretoward tensile residual stress. As can be seen from FIG. 8, coating(a)'s titanium oxide-based layer has a thickness of 19 nm. Because thecompressive residual stress of the silicon oxide and siliconoxynitride-based layers is higher than the tensile residual stress ofthe titanium oxide-based layer, the net residual stress of coating (a),even after heat-treatment, is compressive rather than tensile. Incertain example embodiments, this net compressive stress will result ina more durable coating (as compared to a coating with a net tensilestress). Comparative coatings (b) and (c) show that when the titaniumoxide-based layer is thicker −100 nm in coating (b) and 102 nm incoating (c), after heat-treating, the net residual stress is tensile(demonstrated by the positive σ_(x) and σ_(y) values). The stress valuesfor single layers (i) and (ii) are provided simply to show that theresidual stress of both a silicon oxide-based layer and a siliconoxynitride-based layer is compressive both before and after heattreating. These compressive residual stress values each act to offsetthe tensile residual stress of the titanium oxide-based layer.

From FIG. 8, it will be appreciated that including some layers in thecoating that have a compressive residual stress, even after heating,and/or thinning any layers having a tensile residual stress, mayadvantageously result in a coating having a net compressive residualstress, even after heat-treatment. In certain example embodiments, if alayer prone to tensile stress can be thinned and/or otherwise modifiedsuch that the tensile stress is less than the compressive stress ofother layers in the stack, the overall net residual stress of thestack/coating may be compressive. Therefore, a temperable three-layeredAR coating that maintains durability even after heat-treatment may beproduced, in certain example embodiments, by (1) including layer(s)having a compressive residual stress, e.g., low index layers such assilicon oxide and medium index layers such as silicon oxynitride, and/or(2) modifying layers prone to having tensile stress, such as high indextitanium oxide-based layer(s), e.g., by reducing their thickness to lessthan about 25 nm (more preferably less than about 22 nm, and even morepreferably approximately equal to or less than 20 nm). The foregoingexplanation is by way of example. In other example embodiments, layershaving a net compressive stress (even after heating) may be made byother means.

FIG. 9 is a graph comparing the as-deposited stress and stress afterheating in for coatings (a) and (b) from FIG. 8. FIG. 9 shows thatcoating (a) has compressive residual stress both before and afterheating. FIG. 9 also shows that coating (b) (a comparative exampleincluding a titanium oxide-based layer having a thickness of 100 nm) hasa net compressive stress prior to heating; however, after heat treating,coating (b) has a net tensile stress. In certain example embodiments,reducing the amount of tensile stress present in an overall coating(such as in coating (a)) can help improve the durability of the coating.

Example 2

A temperable AR coating was applied to both surfaces of a glasssubstrate (e.g., a double sided coating was made).

The double-sided coating (as shown in FIG. 3) also maintains its opticaland aesthetic qualities after tempering/heat-treatment processes, whencoated on the Sn side of float glass, without the need for anyadditional surface preparation such as polishing. The coating designdescribed in the preceding paragraphs with respect to Example 1 can beapplied to the second surface (or Sn side) of the glass to reduce theoverall reflection from both interferences.

FIG. 10 illustrates the light transmission achieved with theabove-described design applied to both surfaces of low iron glass beforeand after tempering/heat-treating. The photopic light transmissionincreases after exposure to a tempering environment and exceeds 99% atnormal incidence on 3.2 mm low iron glass.

FIG. 11 illustrates example ranges of physical thicknesses andrefractive indices for temperable AR coating 3 when SiOxNy, TiOx, andSiOx are used for the medium index, high index, and low index layers,respectively. FIG. 9 represents example thicknesses used for each layerin a preferred embodiment of this invention; however, other physicalthicknesses may be used for each of the layers in other instances.

Example ranges for the thicknesses of each layer are as follows:

TABLE 1 (Example Materials/Thicknesses; FIG. 1 Embodiment) LayerRange(nm) More Preferred(nm) Example(nm) SiO_(x)N_(y) (layer 5) 75-135nm 94-115 nm 95 nm TiO_(x) (layer 7)  10-35 nm  12-22 nm 21 nm SiO_(x)(layer 9) 70-130 nm 89-109 nm 105 nm 

In certain example embodiments, AR coatings described herein may be usedon thin, low-iron glass. Example low-iron glass substrates are disclosedin, for example, U.S. application Ser. No. 12/385,318, as well as inU.S. Publication Nos. 2006/0169316; 2006/0249199; 2007/0215205;2009/0223252; 2010/0122728; and 2009/0217978, the entire contents ofeach of which are hereby incorporated herein by reference. In certainexample embodiments, when Example 2 was applied to 3.2 mm low-ironglass, the visible transmission was measured at about 99%. However, thecoated articles described herein may have a visible transmission of atleast about 85%, sometimes at least about 90%, sometimes at least about95%, and still other times even higher (e.g., around 99%), depending onthe desired end-application.

The following tables show the as coated to heat treated color shifts forthe single sided and double sided AR coatings on low-iron glass. It willbe appreciated that the heat treatment processes have a reduced (andsometimes no) appreciable impact on the aesthetic (e.g., reflectedcolor) quality of the coating. The example coatings described hereinhave purple hues as deposited, for example. The example purple hue ismaintained after heat treatment. This is particularly desirable in anumber of applications, where aesthetic quality in terms of reflectedcolor is correspondingly desired.

Example Single-Sided AR Average Color Readings

L* a* b* Y SS Bake Trans 97.92 −0.92 0.77 94.72 SS Bake Glass 25.96 3.99−3.93 4.73 SS Bake Film 25.80 3.94 −3.95 4.68 SS Trans 97.56 −0.83 1.1993.82 SS Glass 26.34 2.75 −3.46 4.86 SS Film 26.02 2.75 −3.30 4.75

Example Single-Sided AR Predicted Color Shifts During Bake

ΔL* Δa* Δb* ΔY ΔE Transmission 0.37 −0.09 −0.43 0.91 0.57 Glass −0.381.24 −0.47 −0.13 1.38 Film −0.22 1.20 −0.65 −0.07 1.38

Example Double-Sided AR Average Color Readings

L* a* b* Y DS Bake Trans 99.47 −1.53 1.42 98.63 DS Bake Glass 6.08 24.93−19.38 0.75 DS Bake Film 6.11 24.91 −19.30 0.76 DS Trans 99.12 −1.362.02 97.74 DS Glass 6.36 19.13 −16.87 0.79 DS Film 6.42 19.31 −16.980.80

Example Double-Sided AR Predicted Color Shifts During Bake

ΔL* Δa* Δb* ΔY ΔE Transmission 0.35 −0.17 −0.59 0.89 0.71 Glass −0.275.80 −2.50 −0.04 6.32 Film −0.31 5.60 −2.32 −0.04 6.07

The layers described herein may be stoichiometric and/or substantiallyfully stoichiometric in certain example embodiments; whereas the layersmay be sub-stoichiometric in different example embodiments. However, itwill be appreciated any suitable stoichiometry may be used in connectionwith the any of the example layers described herein.

Furthermore, in some instances, other layer(s) below, within, or abovethe illustrated coating 3 may also be provided. Thus, while the layersystem or coating is “on” or “supported by” substrate 1 (directly orindirectly), other layer(s) may be provided therebetween. Thus, forexample, the coating 3 of FIG. 1 and the layers thereof may beconsidered “on” and “supported by” the substrate 1 even if otherlayer(s) are provided between layer 5 and substrate 1. Moreover, certainlayers of the illustrated coating may be removed in certain embodiments,and other layers added in other embodiments of this invention withoutdeparting from the overall spirit of certain embodiments of thisinvention. In certain other example embodiments, coating 3 may consistessentially of layers 5, 7, and 9, and layer 9 may be exposed to theatmosphere (e.g., layer 9 may be the outermost layer of the coating incertain example embodiments).

The example embodiments described herein may be used in connection witha variety of applications. For instance, a single-sided AR coating madeaccording to the example embodiments described herein may be used forapplications such as, for example, lights for commercial or residentialareas or at sports or other large venues or arenas, lighting applicationin general, touch screens, etc. A double-sided AR coating made accordingto the example embodiments described herein may be used for applicationssuch as, for example, electronics, displays, appliances, facades, etc.Of course, other applications also are possible for the exampleembodiments disclosed herein.

A coated article as described herein (e.g., see FIGS. 1-3) may or maynot be heat-treated (e.g., tempered) in certain example embodiments.Such tempering and/or heat treatment typically requires use oftemperature(s) of at least about 580 degrees C., more preferably of atleast about 600 degrees C. and still more preferably of at least 620degrees C. The terms “heat treatment” and “heat treating” as used hereinmean heating the article to a temperature sufficient to achieve thermaltempering and/or heat strengthening of the glass inclusive article. Thisdefinition includes, for example, heating a coated article in an oven orfurnace at a temperature of at least about 550 degrees C., morepreferably at least about 580 degrees C., more preferably at least about600 degrees C., more preferably at least about 620 degrees C., and mostpreferably at least about 650 degrees C. for a sufficient period toallow tempering and/or heat strengthening. This may be for at leastabout two minutes, or up to about 10 minutes, in certain exampleembodiments.

Some or all of the layers described herein may be disposed, directly orindirectly, on the substrate 1 via sputtering or other suitable filmformation technique such as, for example, combustion vapor deposition,combustion deposition, etc.

Further Examples

As discussed above, certain materials may result in undesirable colorshifts, ΔE*, between the pre and post-tempered application of an ARlayer. Accordingly, it will be appreciated that there is a need toidentify and integrate materials into three-layer anti reflectivecoatings that maintain (e.g., to the greatest extent possible) thedesired optical properties after exposure to typical heat treating(e.g., tempering) environments.

As discussed above with reference to FIG. 1, for example, certainembodiments may incorporate an AR coating 3 with a medium index layer 5,a high index layer 7, and a low index layer 9. The inventors haveidentified that using materials, such as SiOxNy, in combination with,for example, TiOx and SiOx at certain thicknesses may result in athree-layer anti-reflective coating that better maintains the opticalproperties between the as deposited state and a heat treated or temperedstate.

FIG. 12 is an example of a three-layered temperable AR coating madeaccording to certain example embodiments. A medium index layer 1204 ofor including SiOxNy preferably has a thickness of from about 45 to 85nm, more preferably from about 50 to 70 nm, even more preferably fromabout 55 to 65 nm. In certain example embodiments, the thickness of thelayer of SiOxNy may be about 60-61 nm.

It has surprisingly been found that silicon oxynitride (e.g., SiOxNy)can be deposited to have an index of refraction of from about 1.60 to2.0, more preferably from about 1.65 to 1.9, even more preferably fromabout 1.7 to 1.85 or 1.7 to 1.8, and most preferably from about 1.7 to1.79 (at 550 nm), and will not significantly degrade in its opticalproperties upon tempering and/or heat treatment. Moreover, in certainexample embodiments, a layer of or comprising silicon oxynitride (e.g.,SiOxNy) may produce the following advantages: 1) Small color shift(e.g., ΔE*<3 units), after baking in an air environment at times andtemperatures ranges typical for glass tempering processes; 2) Little tono appreciable degradation in the desired optical characteristics of thecoating after tempering in the visible region of the spectrum; and 3)Little to no appreciable change in the refractive index in the visibleportion of the spectrum after exposure to typically temperingenvironments. Therefore, the inventors advantageously discovered that alayer of or including silicon oxynitride (e.g., SiOxNy) is suitable foruse as a medium index layer 1204 in a temperable three layer AR coating.

In certain example embodiments, the high index layer 1206 is providedover the medium index layer 1204 of the AR coating 1202. The high indexlayer 1206 has an index of refraction of at least about 2.0, preferablyfrom about 2.1 to 2.7, more preferably from about 2.25 to 2.55, and mostpreferably from about 2.3 to 2.5 (at 550 nm) in certain exampleembodiments. In certain example embodiments, a particularly desirableindex of refraction of the high index layer 1206 at 380 nm may be fromabout 2.7 to 2.9 (and all sub-ranges therebetween). In further exampleembodiments, an ideal index of refraction of the high index layer 1206at 780 nm may be from about 2.2 to 2.4 (and all sub-rangestherebetween).

The high index layer 1206 preferably has a thickness of from about 75 to125 nm, more preferably from about 85 to 115 nm, even more preferablyfrom about 95 to 105 nm, and most preferably from about 100 to 105 nm.In certain exemplary embodiments, the high index layer 1206 has athickness of around 102 nm.

In certain instances, it is advantageous that the material(s) comprisingthe high index layer 1206 have a high index of refraction. An examplematerial for use as a high index layer is titanium oxide (e.g., TiOx).The titanium oxide may be stoichiometric TiO₂ or partially oxygendeficient/sub-stoichiometric TiOx in different embodiments of thisinvention. Of course, other materials (including those of or includingTiOx) may be used in different embodiments of this invention.

In certain example embodiments, the low index layer 1208 is providedover the high index layer 1206 of the AR coating 1202. The low indexlayer 1208 has an index of refraction of from about 1.4 to 1.6, morepreferably from about 1.45 to 1.55, and most preferably from about 1.48to 1.52 (at 550 nm) in certain example embodiments. In certain exampleembodiments, an ideal index of refraction of the low index layer 1208 at380 nm may be from about 1.48 to 1.52 (and all sub-ranges therebetween).In further example embodiments, an ideal index of refraction of the lowindex layer 1208 at 780 nm may be from about 1.46 to 1.5 (and allsub-ranges therebetween).

In certain example embodiments, the low index layer 1208 has a thicknessof from about 70 to 130 nm, more preferably from about 80 to 115 nm,even more preferably from about 85 to 105 nm, and most preferably fromabout 85 to 95 nm. In certain example embodiments, the thickness of thelow index layer may be 87-93 nm.

In certain instances, it is advantageous that the material(s) comprisingthe low index layer 1208 have an index of refraction lower than both themedium and high index layers, and in certain example embodiments, therefractive index of the low index layer 1208 may be less than that ofthe glass substrate upon which the coating is provided. An examplematerial for use as a low index layer is silicon oxide (e.g., SiOx). Ofcourse, other materials (including those of or including SiOx) may beused in different embodiments of this invention. For instance, the layermay be a silicon-inclusive layer that is partially oxided and/ornitrided in different embodiments of this invention.

The AR coating 1202 of FIG. 12 may be provided on only one major surfaceof glass substrate 1200 as shown in FIG. 12. However, FIG. 13illustrates an example embodiment where the AR coating 1202 is providedon both major surfaces of the glass substrate 1200. In other words, afirst AR coating 1202 is provided on a first major surface of thesubstrate 1200 and a second AR coating 1202 is provided on a secondmajor surface of the substrate 1200.

Example Anti-Reflective Coating Applied to a Single Glass Surface

FIG. 14 is a graph showing the surface reflectivity comparison of athree-layer AR coating before and after exposure to a temperingenvironment according to certain example embodiments. For example, an ARcoating may be include the following layers in order moving away fromthe substrate: a medium index layer of SiO_(x)N_(y) that is about 60 nmthick, a high index layer of TiO₂ that is about 102 nm thick, and alower index layer of SiO₂ layer that is about 93 nm thick. The ARcoating may be applied to a clear glass substrate of soda lime silicatype glass, and the above layers disposed onto the glass substrate,e.g., by sputtering or other suitable technique. In this example, the ARcoating is provided on only one major surface of the glass substrate(e.g., as shown in FIG. 12). The coating may then be tempered at a maxtemperature of 650 degrees C. Of course, as noted above, the same orsimilar coating may be disposed on the opposing major surface of thesoda lime glass substrate.

As can be seen in FIG. 14, the change in reflectivity response (e.g., %R) between when the three-layer AR is deposited versus after thethree-layer AR is tempered may be extremely small. As noted above, it isdesirable to have a low difference in optical characteristics betweenpre- and post-tempering. In certain example embodiments, the change inreflectivity for a single-sided coating made according to certainexample embodiments of the invention preferably is less than 1% point,more preferably less than 0.5% points, and still more preferably lessthan about 0.2-0.3% points

FIG. 15 is a graph showing 10 samples of the color shift before and 10samples after tempering. The data in the FIG. 15 graph is based on 10samples of the above-described example single-sided AR coating (SiOxNy,TiOx, and SiOx). The measurements were taken with an Illuminate Cobserver at 2°. The table below summarizes the results of the two abovegraphs by averaging the 10 measurements. Data from both Illuminate C andD65 observers at 2 and 10 degrees are provided in the table below.

R_(vis) T_(vis) ΔE* R_(vis) T_(vis) ΔE* As Deposited 4.93 93.3 2.78 4.9593.3 2.48 Tempered 4.75 93.5 4.79 93.5 Illuminant C/2° D65/10°

As noted above, it is desirable to achieve a color shift, ΔE*, betweenas deposited and tempered of less than 3. As can be seen in the abovetable, when using illuminate C at 2° and illuminate D65 at 10° the ΔE*value for the above example 3 layer AR is below the desired ΔE* value of3. Furthermore, both the R_(vis) and T_(vis) optical properties aresubstantially the same or similar pre- and post tempering. Suchattributes are desirable in producing tempered coated articles.

Example Anti-Reflective Coating Applied to Both Glass Surfaces

Certain example embodiments may include the following layers in ordermoving away from the substrate: a medium index layer of SiO_(x)N_(y)that is about 61 nm thick, a high index layer of TiO₂ that is about 102nm thick, and a lower index layer of SiO₂ layer that is about 87 nmthick. This example three-layer AR coating may be applied to a clearglass substrate of soda lime silica type glass and the above layersdisposed onto both sides of the glass substrate, e.g., by sputtering orother suitable technique. In contrast to the above example (e.g., FIG.12), this example AR coating may be provided on both major surfaces ofthe glass substrate (e.g., as shown in FIG. 13). The three-layer ARcoating may then be tempered at a max temperature of 650 degreesCelsius.

FIG. 16 is a graph showing the surface reflectivity comparison of theabove described three-layer AR coating applied to both surfaces of aglass substrate before and after exposure to a tempering environmentaccording to certain example embodiments. As can be seen, the doublesided coating approach may result in a reflectivity percentage of nearzero in some case and may further be below 1 from approximately 460 nmto 660 nm. Further, the “as deposited” reflectively responsesubstantially mimics the tempered reflectivity response. As noted above,it is desirable to have the pre- and post-tempering opticalcharacteristics remain substantially similar. In certain exampleembodiments, the change in reflectivity for a double-sided coating madeaccording to certain example embodiments of the invention preferably isless than 1% point, more preferably less than 0.5% points, and stillmore preferably less than about 0.2-0.3% points

The following table summarizes the optical characteristics pre- and posttempering of the above example three-layer AR coating that may beapplied to both sides of a glass substrate.

Rvis Tvis ΔE* Rvis Tvis ΔE* As Deposited 0.35 97.7 1.42 0.36 97.9 1.44Tempered 0.48 96.9 0.52 97.2 Illuminant C/2° D65/10°

As can been seen coating both sides of glass substrate may result insmall variances in optical characteristics. Specifically, the aboveobserved ΔE* of less than 1.5 quite low. Thus, in certain exampleembodiments that include a double-sided AR coating, certain exampleembodiments may achieve a ΔE* of less than 3, more preferably less than2.5, still more preferably less than 2, and sometimes even lower.

Accordingly, the example three-layer AR coating that incorporates SiOxNyat the medium with, for example, TiOx and SiOx at the above describedthicknesses may result in a reduction in R_(vis) and a very low (andsometimes even substantially no) reflectively color shift.

Changes in optical characteristics (e.g., ΔR_(vis), ΔT_(vis), ΔE*)between the as deposited and tempered states may be further reduced byadjusting the stochiometry of the SiOxNy in certain example instances.Alternatively, or in addition, optical characteristics (e.g., ΔR_(vis),ΔT_(vis), ΔE*) between the as deposited and tempered states may befurther reduced by adjusting the physical thickness of all the layers inthe stack (e.g., the medium, high, and low) in order to shift thespectral curve while maintaining the desired spectral bandpass.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of making a coated article, the methodcomprising: providing a glass substrate; disposing a silicon-inclusivemedium index layer, directly or indirectly, on a first major surface ofthe substrate; disposing a high index layer over and contacting themedium index layer, the high index layer having a thickness of at least85 nm; disposing a low index layer over and contacting the high indexlayer; and heat-treating the substrate with the medium, high, and lowindex layers disposed thereon, wherein the coated article has a ΔE*value of less than 3 between as deposited and heat treated states. 2.The method of claim 1, wherein: the medium index layer comprises siliconoxynitride and has an index of refraction from about 1.8 to 2.0 at 380nm, from about 1.7 to 1.8 at 550 nm, and from about 1.65 to 1.8 at 780nm; the high index layer comprises an oxide of titanium and has an indexof refraction of from about 2.7 to 2.9 at 380 nm, from about 2.3 to 2.5at 550 nm, and from about 2.2 to 2.4 at 780 nm; and the low index layercomprises an oxide of silicon, and has an index of refraction of fromabout 1.45 to 1.55 at 380 nm, 550 nm, and 780 nm.
 3. The method of claim1, wherein the low index layer comprises silicon oxide.
 4. The method ofclaim 1, wherein the medium index layer comprising silicon oxynitrideand has an index of refraction of from about 1.7 to 1.8 at 550 nm. 5.The method of claim 1, wherein the high index layer comprises an oxideof titanium, and has a thickness between about 95 to 105 nm.
 6. Themethod of claim 1, wherein: the medium index layer consists of siliconoxynitride and has an index of refraction of from about 1.7 to 1.8 at550 nm, the high index layer comprises an oxide of titanium, and has athickness between about 95 to 105 nm, and the low index layer comprisesor consists of silicon oxide.
 7. The method of claim 1, furthercomprising: disposing a second silicon-inclusive medium index layer,directly or indirectly, on a second major surface of the substrate;disposing a second high index layer over and contacting the secondmedium index layer, the high index layer having a thickness of at least85 nm; and disposing a second low index layer over and contacting thesecond high index layer, wherein the second medium, second high, andsecond low index layers are disposed on the substrate prior to said heattreating.
 8. The method of claim 7, wherein the coated article has a ΔE*value of less than 2 between as deposited and heat treated states. 9.The method of claim 7, wherein the coated article has a ΔE* value ofless than or equal to about 1.5 between as deposited and heat treatedstates.
 10. A method of making a coated article, the method comprising:providing a glass substrate; disposing a silicon-inclusive medium indexlayer, directly or indirectly, on a first major surface of thesubstrate; disposing a high index layer over and contacting the mediumindex layer, the high index layer having a thickness of at least 85 nm;and disposing a low index layer over and contacting the high indexlayer, wherein the coated article is heat treatable so as to have a ΔE*value of less than
 3. 11. The method of claim 10, wherein: the mediumindex layer consists of silicon oxynitride and has an index ofrefraction of from about 1.7 to 1.8 at 550 nm, the high index layercomprises an oxide of titanium, and has a thickness between about 95 to105 nm, and the low index layer comprises or consists of silicon oxide.12. The method of claim 10, further comprising: disposing a secondsilicon-inclusive medium index layer, directly or indirectly, on asecond major surface of the substrate; disposing a second high indexlayer over and contacting the second medium index layer, the high indexlayer having a thickness of at least 85 nm; and disposing a second lowindex layer over and contacting the second high index layer, wherein thesecond medium, second high, and second low index layers are disposed onthe substrate prior to any heat treating.
 13. The method of claim 12,wherein the coated article is heat treatable so as to have a ΔE* valueof less than
 2. 14. A coated article comprising an antireflectivecoating supported by a first major surface of a substrate, wherein theantireflective coating comprises, in order moving away from thesubstrate: a silicon-inclusive medium index layer disposed, directly orindirectly, on the first major surface of the substrate; a high indexlayer disposed over and contacting the medium index layer, the highindex layer having a thickness of at least 85 nm; and a low index layerdisposed over and contacting the high index layer; wherein the coatedarticle is heat treatable so as to have a ΔE* value of less than 3 15.The coated article of claim 14, wherein: the medium index layercomprises silicon oxynitride and has a index of refraction of from about1.65 to 2.0 at 380 nm, 550 nm, and 780 nm wavelengths, the high indexlayer has an index of refraction of at least about 2.0 at 380 nm, 550nm, and 780 nm wavelengths, the high index layer having a thicknessbetween about 85 nm and 115 nm, and the low index layer has an index ofrefraction of from about 1.4 to 1.6 at 380 nm, 550 nm, and 780 nmwavelengths.
 16. The coated article of claim 14, wherein the mediumindex layer comprising silicon oxynitride and has an index of refractionof from about 1.7 to 1.8 at 550 nm.
 17. The coated article of claim 14,wherein the high index layer comprises an oxide of titanium, and has athickness between about 95 to 105 nm.
 18. The coated article of claim14, wherein a second major surface of the substrate supports a secondantireflective coating that comprises, in order moving away from thesubstrate: a second silicon-inclusive medium index layer, directly orindirectly, on the second major surface of the substrate; a second highindex layer over and contacting the second medium index layer, the highindex layer having a thickness of at least 85 nm; and a second low indexlayer over and contacting the second high index layer, wherein all saidlayers are disposed on the substrate prior to any heat treating.
 19. Thecoated article of claim 18, wherein the coated article is heat treatedtogether with the layers disposed thereon.
 20. The coated article ofclaim 19, wherein the coated article has a ΔE* value of less than 2between as deposited and heat treated states.